In conventional protein mapping, exemplified by the SDS-page technique, differing properties of the proteins are used to separate them out into a two-dimensional map. Typically, proteins acquired from a sample are first separated out according to their isoelectric equilibrium points, by depositing them on a pH graded strip-gel. Under a moderate electric field, the proteins are allowed to establish their isolectric equilibrium points within that gel. The strip-gel is then placed onto the edge of a conventional two-dimensional electrophoresis separation plate in an SDS-page system. A strong orthogonal electric field then causes the proteins to migrate in the second dimension, across the plate, according to their charge/mass ratio. The SDS (sodium dodecasulfate) changes the electrophoretic state of the molecules so that, when they are on the plate, they move at a speed proportional to their charge/mass ratio. The smaller proteins move faster than the larger ones (their mobility in the constant field being higher) and, eventually, one ends up with a two-dimensional or orthogonal separation of the proteins across the surface of the plate. At the end of the separation procedure, each protein appears as a separate spot on the gel.
To undertake further tests on the separated proteins, the individual spots may be dug out of the gel, or otherwise extracted, and investigated for example in a mass spectrometer.
There are a number of problems with this known technique, including the slowness of the separation, the clumsiness of the rather ad hoc procedures required, the fact that many manipulations are needed with the consequent susceptibility to systematic errors, and the impossibility of doing parallel analyses for comparison.
It is an object of the present invention at least to alleviate these difficulties of the prior art.